Peter Cowan/Lexi Cameron wrote:

Perhaps some of you might be interested in my observations taken during today's
test flights. While my homebuilt is close to a Cessna 170, it does vary in a couple
of key areas. The thrust line is over 5 degrees more negative, the empty Cof G is
4" aft of Cessna's forward limit.
Finally got around to making temporary change to thrust line and Cof G to see if
the impact on performance was enough to warrant a permanent change. I raised the
thrust line by putting washers ahead of the lower Lord mount; moved the Cof g
forward by first shifting the battery and next by dumping 100lbs of water into the
forward float compartment. Yes, I did the arithmetic first.

One comment on the Lord mounts  is that the half taking the load was compressed a
good 1/4" compared to the other half.  The attach points are about 10" apart so
that is about 1.5 degrees due to squeezed rubbers (maybe 3 if you include the
distortion in the top ones.)
Most flights were made with no cowl on but I did add a temporary top to the baffles
to ensure cooling.

Unfortunately, the results were not as dramatic as I would have predicted. The 5
degree thrustline change was almost unnoticeable but that could have been
attributed to the added drag of no cowl.

The C og G move was also Ho Hum. All the flights were off water and I expected some
forward pitching on landing but found none. It did run out of back trim which will
be fixed by another change: another degree of neg stab incidence. There was a
noticeable difference in rising onto the step.

Overall, the experiment just demonstrated that measurement is not very easy.

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